FIG. 6 illustrates a conventional electric motor. The electric motor includes an electric motor shaft 1, a rotor 2 which is rotated about the electric motor shaft 1, a stator 3 disposed around the rotor 2, a casing 4 which accommodates the rotor 2 and the stator 3, and a cover 5 to be mounted on one axial end of the casing 4. The electric motor is installed in such a vertical posture that the electric motor shaft 1 extends vertically, such as a slewing electric motor for an excavator. In the following, the conventional art shown in FIG. 6 and the embodiments of the invention to be described later are explained based on the premise that the electric motor is installed in the above posture and the electric-motor axial direction is vertical. Besides, the term “electric motor” in the present specification includes a generator and a generator-motor based on the same principle as applied to an electric motor in the narrow sense, in addition to the electric motor in the narrow sense.
The cover 5 is mounted on the upper end surface of the casing 4 by not-graphically-shown bolts. The upper and lower portions of the electric motor shaft 1 are rotatably supported on the cover 5 and the lower portion of the casing 4 via bearings 6 and 7, respectively.
The stator 3 includes a stator core 8 constituted of electromagnetic steel plates laminated one over another and a stator coil 9 wound around the stator core 8 vertically (in the electric-motor axial direction shaft: hereinafter, it may be called as the electric-motor axial direction). The stator coil 9 includes a pair of coil ends 9a which are respective upper and lower folded portions of the stator coil 9. The stator coil 9 is wound in a state that the coil ends 9a protrude in the electric-motor axial direction beyond respective axial end surfaces of the stator core 8.
The stator 3 is inserted into the casing 4 after the coil is wounded. The casing 4 is covered with an upper die so as to be used as a receiving die (a lower die). Through the upper die, a sealant 10 is injected into the casing 4 to fill the casing 4. The sealant 10 is composed of, for example, synthetic resin material such as unsaturated polyester resin having an electric insulation property and a thermal conductivity. The sealant 10 is thus provided so as to cover the entirety of the stator 3 or a part of the stator, the part including the coil ends 9a, to enhance the thermal conductivity from the stator 3 to the casing 4 (see patent literature 1). The sealant 10 is injected with a certain pressure which allows the sealant to be securely infiltrated into a portion required to be sealed, such as a space between the stator coils.
To the coil ends 9a in the electric motor is connected a not-graphically-shown lead wire for interconnecting an external wiring and the stator coil 9. The lead wire is drawn out through a through-hole formed in the peripheral wall of the casing, connected to a terminal block provided in the outer peripheral wall of the casing. As a structure for drawing out the lead wire, generally known is one disclosed in patent literature 2. The structure includes a seal member (a grommet) filled in the through-hole. The seal member surrounds a lead-wire insertion hole located in the center thereof, and the lead wire is drawn through the lead-wire insertion hole.
The above structure, however, has a possibility of allowing the sealant 10 injected into the casing 4 to leak out through the lead-wire insertion hole of the seal member or through the gap between the seal member and the circumferential surface of the through-hole, due to an injection pressure (a fluid pressure). The leakage of sealant reduces the injection pressure to deteriorate the stator sealing effect. Besides, the leaked sealant may intrude into the terminal block to deteriorate the electric insulation property.